Foundry core composition



Patented Apr. 4, 1950 FOUNDRY CORE COMPOSITION Thomas E. Barlow, Jackson, Ohio, assignor to Eastern Clay Products, Inc., a corporation of Maryland No Drawing. Application November 6, 1947, Serial No. 784,528

3 Claims. (Cl. 22-188) My invention relates to foundry compositions, especially to foundry cores and to a method of producing the same.

One object of my invention is to provide a method of producing both foundry core compositions and the foundry cores formed therefrom, which method is at once simple, rapid and certain in its results, appreciably minimizing the time heretofore required, employing only a small number of procedural and manipulative steps, requiring only modest labor demands of but limited skill.

.Another object is to provide a foundry core composition which is quickly produced from materials which in themselves are. comparatively readily available and inexpensive, which composition is characterized by the substantial absence of evolution of gas during the pouring of the casting, in which the sand can be of required coarseness without detrimental effect upon the surface of the finished casting, and which displays required green strength with high degree of hardness in the finished core, and'by the use of which clean, sound castings are produced, faithful in detail to that of the pattern' Yet another object is to provide a foundry core which is readily and rapidly formed, which core displays required high green strength and moldability with required hardness of the finished core, with achievement of excellent surface detail in the poured casting without necessity of employing a core wash, and in which a moderate quantity of argillaceous substances may be included along with the clean silica sand without detrimental results.

Other objects of my invention in part will be obvious and in part more fully pointed out hereinafter, during the course of the following description.

My invention accordingly resides in the combi nation of substances, mixtures of materials, and compositions of ingredients and in the several manipulative steps, and the relation of each of the same to one or more of the others, the scope of the application of all of which is more fully set forth in the claims at the end of the specification. i

As conducive to a more thorough understanding of my invention, it may be noted at this point that in foundry practice certain problems are encountered in' the production of foundry cores which are peculiar to them and are separate and apart from those encountered in the production of mold compositions in general.

Since it is these cores which determine such internal openings as are within the casting, it is in large measure possible to provide the necessary support for them only at the ends of the cores, where the mold is received within the flask.

Moreover, to produce sound, firm castings, the core must have baked strength sufficient to withstand the weight of the poured metal, and must thereafter be subject to collapse when the metal shrinks as it passes through its recalescence point.

' Ordinary silica sand itself does not give rise to a core sufllciently hard or strong to satisfy these requirements. Thus the practice has arisen, some years ago, of employing a drying oil mixed in small quantity with ordinary silica sand. Such oil is highly expensive by comparison with the cost of the'sand and the use to which the mold is put. Accordingly, it is of course desirable to minimize, in so far as is possible, the quantity of oil required. Moreover, experience has disclosed that while the mixture of drying oil and silica sand will bake to a core of requiredhardness, such mixture displays the undesirable characteristic of low green strength and unsatisfactory moldability. Thus, it does not accommodate itself readily to the surface details of the pattern as it is rammed in position thereabout. Similarly, when the core is characterized either by massive section or lon span, or both, there is danger of collapse under its own weight.

While the addition of fine sand, sand containing a small quantity of clay, or clay itself will give rise to higher green strength, experience discloses that the use of such materials notably increases the requisite quantity of oil for given baked strength. Because of the high costs of these materials, this expedient has been discarded for all practical purposes. The more usual recourse in developing green strength resides in the addition of some cereal binder, usually corn flour. Here again, practical difficulties are encountered.

Cereal binders give rise to excellent green strength, with 'but little effect on the quantity of oil required for desired baked strength. Two very substantial disadvantages exist, however. One of these is the high cost of cereal binders.

The other, characteristic of such materials, is

that they evolve extremely large quantities of gas during the process of pouring the casting. The likelihood of blow holes incident upon such excessive generation of gas constitutes a very serious problem. A still further disadvantage of the use of cereal binders is that a substantial quantity of water must be added in order to develop the strength of the binder. The driving off of this water involves an important factor in increasing the time of baking the casting. This increases both labor costs and investment in plant.

Similarly, it has heretofore been suggested to employ thermal setting resins such as coal tar pitch and gilsonite for increasingthe baked strength of the core. These additives appreciably contributed to the baked strength when converted or hardened, i. e., set, by 'the application of heat. When such thermal setting resins were employed, however, cereal binder still had to be added in order to impart requisite green strength to the core. A further principal objection to the use of thermal-setting resins is that such resins, having hardened, may make it extremely difficult gives rise to notable advantages. I prefer to incorporate a dry powdered resin with clean silica sand in a mixer in an amount of about 96 to about 2% by weight. Sumcient water is added to give rise to a workable mix, whereupon the core oil is included as a final additive. A clean working sand mixture is produced, displaying satisfactory green strength. To permit ready omparison of the composition of the new mix to shake out the core from the casting. Cracked it not form any gummy residues thereon. Thesev properties are had with the coarser sands. Since the cores form the interior portion of the castings, it necessarily follows that because of their restricted location opportunity is minimized of venting to the atmosphere those gases evolved in pouring.

When, however, the molten metal is poured against this coarse, open and permeable sand,

some of the metal penetrates into the core. Upon viewing the poured casting resulting fromthis procedure, it will be found to be both unsightly and rough. Moreover, should this entrained sand be held tightly by the metal it may not be entirely removed in the subsequent cleaning processes, and will remain as a possible cause of damage during subsequent use. Particularly is this true if the space being cored out is intended as an oil or water passage. The practice has arisen therefore of coating those cores which are to be used in difficult locations with a fine refractory material known as core wash. This wash is suspended in water, and this water must be removed by drying. Accordingly, the use of core washes is costly in three-fold respect: in the materials employed, in the labor used in coating, and in the second drying operation which is required.

An important object of my invention therefore is to remove in substantial measure the several disadvantages and defects heretofore confronting the art, and at the same time avoid the necessity of using cereal binders, reducing the quantity of drying oil required and avoiding the according to the practice of my invention with that of a conventional mix heretofore employed. and of the most important qualities resulting from such composition, the following tables are provided:

TABLE I Composition Conven- Ingredlents tional Mix Per cent Conven- Iropcrties tionallMix New Mix #2 Green Compression Strength .6 lb. 1. 3 lb. Permeability 134 129 Dry Tensile Strength Baked 2 hrs.

Study'of the foregoing tables brings forth certain important conclusions. Notably, it will be seen that the expensive and gas. forming ingredient, cereal flour, is eliminated in the new mixture. This is because the inclusion of the resin appears to create suflicient green strength and to confer a cleaning action to the core sand, so that the latter does not adhere, in. the baked core, to the poured metal. When about by weight of resin is employed, no core wash being used, I have found the resultant casting to be as clean as those made with the conventional mix, when the finished core was coated with a core wash. Moreover, when the percentage of resin in the new mix was increased to about 0.9%, I found the resulting casting to be much cleaner and to have much better surface detail than was produced where the core comprised a conventional mix subsequently coated with a core wash.

A further direct advantage attendant upon the practice of my invention is that the consumption of the expensive core oil is reduced by about 25% with actual increase in the dry strength of the resultant core.

I find that, as an additional important advantage attendant upon the practice of my new invention, while foundries are now required to use clean or clay-free sands for the core oil to'function efliciently the clay appears to prevent proper coating and adherence of the core oil to the grains of sand-such is by no means the case where resin additive is employed according to the teachings of my invention. With the resin present, I find that not only does the presence of a small quantity of clay introduce no detrimental effect but, on the contrary, that such additive actually might prove advantageous. Thus in one foundry where my new process is in am ne actual use, a sand containing about 0.75% clay is employed. Nevertheless, the amount of core oil required for adequate baked strength is still about 22% less than when clean sand is employed in a conventional mixture.

The resin, while by comparison with sand is moderately expensive, does not represent such element of expense as would be prohibitive in Where labor costs are not too great, or where the forming of the cores does not constitute a bottleneck in the manufacturing technique, it is entirely satisfactory to use the very small percentage of resin additives suggested in the table included hereinbefore.

Where, however, labor costs are high or production is limited by core-drying facilities, it becomes important to reduce the time required for drying the cores. Ifind that if I increase the percentage of resin in the mix, I achieve a notable reduction in the time of drying. Thus, without appreciable increase in cost, savings are achieved which are important in foundries of the type just discussed. Using the same mixtures as listed in the practice of my invention according to Table I, I find that by increasing the resin content mixture #2 to 2%. giving a mixture designated as #3, the following results were achieved:

Thus, without more, and'by' way of summary,

it will be seen thatthe practice of my invention is attended by the following important advantages, amongst others; the use of corn flour being eliminated, the evolution of gas is appreciably reduced. This results in greater surety in use, and as well permits the use of finer sands, ensuring better surface finish on ,the casting. The

reduction in the moisture content of the core means shorter baking time and lower costs. The quantity of costly core oil employed is reduced a full 25%. The use is entirely eliminated of the costly core washes.

It will be noted that in the practice of my invention, the requisite green strength is imparted to the core by the resin instead of by the cereal binder. Without being bound to such explanation, it may be that the higher green strength is imparted due to the core oil softening the surface of the resin, thereby creating cohesion between the particles. As has been suggested, when the use of cereal flour is eliminated, the quantity of water is reduced. Moreover, the evolution of gas during pouring. is appreciably minimized. Although I do not desire to be bound by such theory, it may be that the resin has some effect upon the rate of drying of the core oil and the speed of setting of the latter. Where a high carbon resin is employed, which I prefer according to the practice of my invention, the elimination of costly core washes may be in part attributed to the creation of a reducing atmosphere by the high carbon content of the resin when the casting is poured.

Moreover, quite contrary to the experience enlow melting point. Accordingly, to avoid difllculties in handling during warm weather, I sometimes find it necessary to undertake to reduce the percentage of oily constituents and to increase the melting point thereof. This I can accomplish by blowing the resin with air or by washing it with butane.

A typical resin suitable for my purpose will be combustible at temperatures ranging from 600 F. and is not converted physically at lower temperatures. Combustion is substantially complete at these temperatures, and no pitch or tarry residues remain in the sand. Only such resins should be used as are of high carbon and low hydrogen content. As has been stated, the high carbon content creates a reducing atmosphere in the region of the core, and by minimizing oxidation of the poured metal, it tends to yield clean castings.

To insure that the resins ignite when first entering the zone of combustible temperature, I sometimes find it desirable to catalyze the resin by the addition of a metallic oxide. When catalysts are added, I find it advantageous to introduce them in quantities of about $4; of 1% to about 1% by weight of the resin; Suitable catalysts are oxides of manganese, chromium,

copper, nickel, vanadium, cerium, silver, iron and cobalt.

A core composition of the type described appreciably reduces the quantity of expensive core oil which is employed, while maintaining the requisite baked strength. Important decrease in the quantity of water which is requiredis effected, thereby shortening the baking time. Necessity for the use of a cereal binder is eliminated. With it passes the excessive evolution of gas during pouring, a highly detrimental phenomenon which attends upon the use of cereal binder and which frequently results in blow holes in the castings, thereby appreciably contributing towards a high percentage of reiections.

With the new composition, substantial green strength is achieved. Moreover, coarse permeable sands may be employed, facilitating rapid venting. Also, I find less adherence of the sand to the adjacent surface of the casting. This is probably due to a reducing atmosphere created by the high carbon content of the resin. In any event, and regardless of the precise explanation of this phenomenon, the necessity of core wash is avoided. Attendant upon this is the saving in materials, labor costs, and drying off the water vention' displays green strength adequate to hold up properly in the baking oven. It has baked strength suflicient to withstand the loads to which it is subjected in the casting operation. At the same time, its strength is such that it collapses properly upon shrinkage of the surrounding casting during the, cooling process, so that no localized overstressing of the casting results and no failure of the latter is encountered.

The method itself, both of producingthe core composition and of producing the cores by the use of such composition, is extremely simple; requires the use of but simple and rapid manipulative steps with minimum requirement of labor; and employs materials which are readily available in the art andinvolve no substantial ele-- ment of expense.

While I have stated that the dry powdered resin may be added to the sand in a mixer, the water thereupon being added with the core oil constituting the final additive, it is of course to be understood that the sequence of additions of introducing the ingredients into the mixture is not intensely critical, and entirely satisfactory results can be achieved by varying the order of introduction. Thus, to illustrate, water may be added to the powdered resin, and the water suspension thereupon added to the dry sand. The core oil may be added at any stage of the operation. My experience discloses, however, that optimum results are achieved by the practice as hereinbefore set forth.

Since many'possible embodiments may be made of my invention, once the broad aspects thereof are disclosed, and since many changes may be made in the embodiments hereinbefore set forth, I desire it to be understood that all 8 ranging from 600 F'., and about 1% tempering wa r.

2. A foundry core composition of high green strength, high dry strength, good permeability and low burn-on properties and consisting essentially of an intimate mixture of about 1% core 011, about 1% water, about .5% to 2% powdered non-thermal setting synthetic resin of high-carbon and low-hydrogen contents and having a low melting point and being combustible to substantial completeness at temperatures ranging from 600 F., and remainder substantially all sand.

3. A foundry core composition of high green strength, high dry strength, good permeability and low burn-on properties consisting essentially of a mixture of about to 97 sand, about 1% core oil, about 1% water, and about .5% to 2% powdered non-thermal setting resin of highcarbon and low-hydrogen contents with metallicoxide catalyzing additive selected from the group consisting of oxides of maganese, chromium, copper, nickel, vanadium, cerium, iron and cobalt, said catalyzing additive amounting to about 54% to 1 by weight of resin.

' THOMAS E. BARLOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,778,329 Mason Oct. 14, 1930 2,047,297 Stahl July 14, 1936 2,101,330 DeLaney Dec. 7, 1937 2,131,205 W'ells Sept. 27, 1938 2,256,832 King Sept. 23, 1941 2,274,618 Remy Feb. 24, 1942 2,289,709 Kelley July 14, 1942 2,409,437 LaCrosse Oct. 15, 1946 2,444,413 Weston July 6, 1948 FOREIGN PATENTS Number Country Date 534,202 Great Britain Feb. 13, 1942 OTHER REFERENCES Pragofi Properties of Resin Bonded Cores," vol. 47 of Transactions of American Foundrymens Association, pages 9'1, 98, and 111. 

2. A FOUNDRY CORE COMPOSITION OF HIGH GREEN STRENGTH, HIGH DRY STRENGTH, GOOD PERMEABILITY AND LOW BURN-ON PROPERTIES AND CONSISTING ESSENTIALLY OF AN INTIMATE MIXTURE OF ABOUT 1% CORE OIL, ABOUT 1% WATER, ABOUT .5% TO 2% POWDERED NON-THERMAL SETTING SYNTHETIC RESIN OF HIGH-CARBON AND LOW-HYDROGEN CONTENTS AND HAVING A LOW MELTING POINT AND BEING COMBUSTIBLE TO SUBSTANTIAL COMPLETENESS AT TEMPERATURES RANGING FROM 600*F., AND REMAINDER SUBSTANTIALLY ALL SAND. 